docs: def _get_database(self, options):
          """Get the database to restore."""
          database_name = options.get('database')
          if not database_name:
              if len(settings.DATABASES) > 1:
                  errmsg = "Because this project contains more than one database, you"\
                      " must specify the --database option."
                  raise CommandError(errmsg)
              database_name = list(settings.DATABASES.keys())[0]
          if database_name not in settings.DATABASES:
              raise CommandError("Database %s does not exist." % database_name)
          return database_name, settings.DATABASES[database_name]